Directional receiver



Sept. l5, 1936'. A. LElB 2,054,160

' DIRECTIONAL RECEIVER Filed June 14, 1932 2 Sheets-SheeI 1 INVENTOR AUGUST LEIB ATTORNEY I Sept. l5, 1936. A L ElB 2,054,160

DIRECTIONAL RECEIVER Filed June 14, 1932 2 Sheets-Sheet 2 INVENTOR AUGUST LEIB ATTORNEY Patented Sept. 15, 1936 UNITED S ES ATENT OFFICE DIRIIC'IIONAL RECEIVER Germany Y Application June 14, 1932, Serial No. 61.7,159V2V In Germany July 16, 1931 3 Claims.

This invention relates to radio direction-finder, especially adapted to aerial craft, comprising one directional and an additional (directional or nondirectional) antenna and means insuring rhythmic change-over thereof.

.In describing applicants novel method of and means for determining the direction of a source of signalling energy reference will be made to the drawings attached to this application and forming a part thereof. In the drawings Figure 1 shows a directional receiver circuit arranged in accordance with the present invention; Figures 2, 3, and 4 illustrate the operation of the arrangement of Figure 1; Figure 1a and 5 illustrate modifications of the arrangement of Figure 1; Figure 6 illustrates the operation of the arrangement of Figure 5 and Figures '7 to 9 inclusive illustrate the mode of operation of the novel arrangements of Figs. l, 1a and 5.

It has been previously suggested in theart to feed the receiver apparatus of the direction-finder from two aerials so as to insure a preciser determination of the direction of the incoming beam. The said two aerials may consist of two crossed loops which alternately, at a rapid rate or rhythm are connected with the receiver, or else one of the aerials may consist of a directional loop or coil antenna, and the other one of a nondirectional linear .antenna feeding the receiver at the same time though in such a manner that their sense of connection is reversed at a rapid rate.

A .similar direction-finding scheme is reproduced in Fig. 1 of the attached drawings for the sake of affording a clearer understanding of what is set forth further below. Referring to Fig. 1, a denotes a non-directional straight antenna, b the winding of a directional loop aerial. k1 is a reversing switch (double-pole switch) 'adapted to connect the antenna b at changing polarity in reference to the antenna a; e is a receiver, which may include signal demodulating means, d a suitable detector connected in the output circuit thereof and whose current is fed by way of a mechanical commutator (reverser) k2 operating in synchronism with the change-over switch k1 into a direct current indicator instrument g with central zero. The two synchronized throw-over switches Ak1 and k2 most suitably may be controlled from an A. C. generator c electrically. The operation of the arrangement is as follows:

Referring to Fig. 2, let b be the position of the directional loop aerial, for example; loop b of Fig. 1, mounted in .an aircraft and having directional characteristic BB, and circle A the characteristic of the non-directional antenna a. The resultant directional characteristic of the two aerials, for one sense of coupling, is represented by the curve Dl and for the other direction of coupling by curve D2. Suppose the direction of travel of the airplane is indicated by the arrow or. If the beacon to be received has the direction mo' then the incoming signal volume, for one sense of coupling of the antenna will be measured by the distance ol, and for the opposite coupling by the distance ou. This results in a detector current having a shape as shown by graph I in Fig. 3, the smaller values zzcorresponding to the resulting current when the two antenna currents oppose, and the larger values i1 to the resulting current when they add. Under the action of the reversing switch k2 the current flowing through the direct current indicating instrument y has a shape as shown in curve i i, Fig. 3. Since i1 is greater than i2, the needle z of the indicating instrument will be kicked out of its central position,V say, towards the right-hand side, and this the pilot interprets as meaning that the source of the signals is located on the right of his direction of travel. If the course Iis to be set for the source of the signals the pilot must steer to the right until the directions or and om coincide. In this instant the directional antenna is at right angles to the beam and becomes ineffective. Hence, the incoming Volume independently of the reversing of the switch k1, is measured by the distance op, and the needle of the direct current instrument g is returned to the Zero position.

It can be similarly shown that when the direction of the incoming beam is qo the needle of the instrument y will be deflected to the left-hand side. Hence, when the pointer occupies the zero position this means that the transversal axis of the loop b points exactly at the transmitter.

The direction-finder arrangement as hereinbefore described and similar ones comprising two aerials and means for reversal of connection are thoroughly suited for checking up on the course of a trip in the absence of wind. But when there is a drift the following complication enters. If an airplane A (see Fig. 4) is to travel in the direction AS with course for the beacon S, and if the velocity of the Wind is equal to BC then, in order to compensate for the drift BC, the pilot must set his course for AB. In order to maintain this course for wind of a certain strength, in an arrangement for direction-finding as before described, the pilot must so turn the loop aerial relative to the aircraft that its transversal axis is directed towards the transmitter S. This rotatory mechanismtends to complicate the equipment, not to speak of the fact that it represents additional ballast, and this Ymiltates against the prevailing aim to reduce both weight and volume in aircraft, not to mention this further circumstance that in a rotatable loop the protective tube provided to surround its Winding can not be made streamline in shapeV seeing that its orientation in reference to the vdirection of the wind changes inA accordance Vwith its angle of rotation.

VIn order to overcome these diiiiculties ar-v rangements according to this invention are so made that the line of zero' reception or volume' i. e., for a direction of the beam where-the indicating instrument YShows no deflection, is'rnade rotary relative to the transversal axis of the loop According to this invention V.this is aerial b. accomplishable by providing means whereby' the Vrelation between the current impulse produced upon the indicator'instrument in one position Yof fthe .antennaandthe. impulse in the opposite connection-istmade variable or adjustable. For this purpose twodiierentways and meansmay be applied: (1).;theratiobetween the impulses can'. be regulated ,byV the adjustment of the ratio between the corresponding current strengths by inserting at the. points a: and ofFigure l v.of the leadsbroughtto the indicating instrument y suitableyariable.resistances X as Ashown in Figllrdlawith the resistances set at different values.

YA(2).;IIhe ratio 4betweenimpulses may berregur- Y, latedlandV made. unequal by ,adjustingv the duration ofi-the current impulses., i..e., the relation between the length in time the switch K is iin one position and thetime 'that said switch is in the other. Forinstance, ifin .the case;of a directionalY characteristic as shown ,in Figure 2 the zero indicationlof :the vinstrument vy' is to correspond to the direction mo ofthe loeam,'arrange mentscould bemade so that. theconnection where the incoming volume is. measuredby the distanoe im lasts som-eglongerV time, and the connec-tion `corresponding to volume .Oq. some shorter ing) ,cnntactK: as shown in the prior igures,` theoperating winding W thereof being energized from vanalternating lcurrent source. Suppose that the positive direction` of the alternating current corresponds tothe throw of ,thereversing contacttowards'therleft-hand side, and the negative sense fof the controllingy alternating current toV Vthe Vchange oir thecontact towards therighthand'side.V .The Pfiods of time T1 and T2 ofthe left- *and the right-hand contact positionsY are alike, iitheapositivve and thenegative energizationof the relay ,is-symmetric as to time. If,l as indicated in Fig.V 6 an additional direct current energization Yis superposed upon, the alternating current excitation,fsaid supplemental excitation being takenfeg., from a potentiometer P fed frorna direct current source N,Vthen, by suitable setting of the contact point F (Fig.5) it is always feasiblel to obtain lthe desired ratio between the ,axisV y, JJ', the indicatorneedle period T1 of resultant positive excitation and the time T2 o1" the resultant negative excitation of the relay. Hence, zero indication of the controlling instrument g can b-e insured at will no matter what the direction no of the beam for a directional characteristic as shown in Fig. 2. Since each and every direction no as the line of zero reception or volume of the check-up apparatus Y corresponds to a definite adjustment of the relation between the times or periods TizT and since this ratio is absolutely a function of the position of the contact slide F of potentiometer P, it rol- `lows that the latter can be calibrated to read in terms of the angle of direction a (see Figs. 2

Yand ll) so that, in order to preserve direction or course all that' is necessary to do is to shift the slide Fintothe corresponding position as indicated .on the scale of the potentiometer P.

Hence, in an arrangement of the invention as hereinbefore described, in order to check-upy on the course to be .kept in the presenceof winds of varying velocities or strength, it is not necessary .to turn .the coil antenna relative to the aircraft; indeed, the. same may be mounted stationary therein in such a way that its transverse axis of parallel to the Ylongitudinal axis of the craft. Distinct mechanical means for rotation are dispensed with, and the protective sheet or tubing surrounding the Vturns of the .loop aerial can be formed stream-line.

AThe direction nders as describe-d above may, in accordance with the present invention, be operated to obtainsense of direction as Well as line of direction. 'I'his operation has been illustrated in Figures 7., 8,and 9 of the drawings.

In Figure '1 theY graph A denotes the directional characteristic of a coil antenna positioned at right ,angles to the axis y, y', and B Ythe characteristic of a non-directional antenna, the assumptionbeing made that the radius of the circle B is equal to the vdiameter of each circle A, although this need not necessarily be true. If the ,loop andyertical antennae are connected in one sense by Ici, the resulting energy may be represented by cardioid C. If the direction of connection of one of the two aerials be reversed, then Vthe cardioid C' will represent the characteristic of the system. v If the beacon beam has the direction SO, then, in one connection of the antenna (cardioid C) there is obtained an electromotive .force measurable -by the distance OM and in the other connection of the aerials an electromotive force measurable by Olli.` These electromotive i'orcesact alternately, .at avery high rate of rhythm, upon a receiver outt comprising a rectifier whose output direct current is reversed in Vsynchronis'm with the antenna reversai; see Figure l, and act upon an .electrodynamic `or an electromagnetic indicator instrument. These impulses may be measured by the distances OM and 'OL, respectively. The resultant eiect is determinable by the distance LM. Iffxthe direction of the beamY SO coincides with the direction y, y of the transverse axis of the coilv antenna, then the needle of theV indicator instrument will not be deflected out of its middle position. f .But if the transmitter, as indicated in Figuref?, is on theV right-hand side of the axis y, y', then the' indicator hand will be "caused to' `kick towards the right. If the transmitter, howevenhappensto belocated totheleft of the will bev thrown ytowards theleft-hand side. Y

"The indicator needle will deflect towards the rightv alsok .whenl the beacon lbeam has the direction S70.; In ordergto: ascertain whetherthe beam comes in from the.frontin the direction SO, or from the rear, direction. SO, all the pilot has to Ado is, to, turn his `direction iinder loop. If the loop is built stationary inside the craft, he must veer his plane towards the right-hand side. As a result the coordinate system .'r, and y', y with the directional characteristics referred thereto `are turned in clockwise direction. `I f the beacon beam has the direction SO the length ML will approachthe point K, in

` other words, it is reduced in size and the deecsible to tell whether the trans'mitter'stationv is located in front or in the rear.

Electrodynamic or electromagnetic instruments for visible reading are less `sensitive than the head phones of an auditory direction finder. Hence, direction finder equipment using visual indicators need higher amplication. Another point is that indicator instruments comprise deflection ranges or kicks which correspond only to certain `intervals of the energy inputs. Hence, they must often be re-set in practice so as to adapt their sensitiveness to different field intensities of the beams, and these volumes are a function both of the distance and the power of the transmitter station. The telephone, on the other hand, responds to the whole energy range from the smallest up to the largest volumes. Hence, it can be used without being altered or adjusted for the greatest as well as the smallest distances for which direction nding is still required.

According to the invention the direction nder in which use ismade of two symmetric cardioids by alternate change-over of two aerials may be rendered more serviceable by making the energies represented by the two cardioids acoustically identifiable so that they may be distinguished by use of the phones shown dotted in Figure 1 rather than by causing the impulses due to the two cardioids to act upon an integrating instrument. This may be accomplished by identifying one of the cardioids by a long dash, and the other one by means of two short dashes. For instance, if the volume of the long dashes corresponds to the length of OM, see Figure 7, and the volume of the subsequent pairs of short dashes to the length of OL, in other words, if the long dashes are louder than the short ones, this means that the transmitter is located towards the right of the axis y, y. If the volume of the short dashes predominates, the transmitter is situated on the left. Moreover, if the pilot has ascertained that the transmitter is located on the right hand side then, if when he turns the loop or the whole plane to the right, the diierence in the Volume of the two signals or impulses diminish, this means that the transmitter is located in front, whereas when they increase the transmitter is in the rear.

To regulate the sharpness or clarity of identication and obtain a more precise determination of the -direction of the beam it is possible to use weaker signals where smaller distances between the receiver and the transmitter are dealt with. Regulation of th'e electromotive forces which are derived from one of the two receiving antennae, say, the non-directional, in-

aerial must be made large, or else a greater clarity of identiiication of the signal. In the latter case the electromotive force from the nondirectional aerial shouldbe chosen small. Since the two cardioids C and C then will change their shape in a similar manner and remain also symmetric in relation to each other it follows that where great variations of the electromotive forces of the two aerials are concerned the characteristic y', y, willfinvariably preserve its position in reference to the direction finder.

The inuence of the regulation of the electromotive forces of the aerials on the clearness of identification may be explained in the following way:

As the radio beacon or beam SO approaches the direction y, y' of the characteristic,n the length of LM becomes smaller and smaller and finally shrinks to a point K when the transmitter falls in the line y', y. Inversely will the same distance and its length be found to grow in proportion as the beam deviates from the line y', y, and such departure will be identifiable so much more sharply the faster this growth takes place; in other words, the acuter the angle TKT between the tangents of the two cardioids at point K as the apex becomes. Under conditions as shown in Figure 7 the said angle amounts to 90 degrees. The electromotive force due to the non-directional antenna (radius of circle B) is equal to the crest electromotive force due to the loop or coil antenna (diameter of the circles AA). Now, if for smaller distances from the radio beacon station the electromotive force due to the non-directional aerial is adjusted to, say, one-half of the previous amount, the two cardioids will assume a form as shown in Figure 8. The angle TKT between the tangents at point K becomes smaller (approximately 53 degrees) and the sharpness of identication grows.

For great distances where sharp identification direction finding is unnecessary it is possible to raise the electromotive force due to the nondirectional antenna, as shown in Figure 9. The radius of the circle B is chosen twice as large as the diameter of the circles AA. The cardioids CC' approach the shape of a circle, their areas become increasingly larger, and the range is correspondingly extended, but the sharpness is smaller seeing that the angle TKT has here grown to 127 degrees.

The direction finder here disclosed is useful both for the waves of relatively great length that have heretofore been used in practice as well as for short and ultra-short waves.

What is claimed is:

1. A device for indicating the direction of a source of radiant energy comprising a loop aerial including an inductance having a grounded tap intermediate its terminals, a polar relay having a movable contact and two stationary contacts disposed on opposite sides of said movable contact thereby to make contact therewith first in one position and then the other, one of said stationary contacts being connected to one terminal of said loop aerial and the other stationary contact being similarly connected to the other terminal of said loop aerial, a connection between said vertical aerial and said movable contact, a receiver coupled to said inductance, a utilization circuit including indicating means for differentiating between the relative intensities of said radiant energy when received during certain intermittent time intervals in respect to such energy when received during intervening ftirne: intervals, means including a potentiometer having amovable contact member'thereonand aJWind 'driftl correction scaleV member` cooperatingk with said contactfmember for applying to s aidindicating Ameans a correction due tao-Wind Y drift,wa current reversing switch in circuit'between said receiver-wand said Vindicating-rneans, and means including a .sourceof "alternating Y i current for actuating said polar relay and said reversing ,switch synchrcnously;, i i i Y 21A device for indicating the direction/cfV a sourcef'of radiant energy comprising,Y afloop Y aerial, a vertical aerial, means including a switch ini. circuitfwitla the windings of said polar relay and a bia-sing source across which saidy potentiometer isconnected., Y

A ,13.7K radiordirection iinder including a directional and al nonfdirectional antenna, a magnetic relay including an amature connected with Vsaid non-directional antenna, contacts connested with the terminals of said directional antenna whereby movement of said armature will connect said non-directional aerial alternately t0 the terminals ofr said` directional aerial, a receiver lcoupled to said aerials,x indicating means, circuits including switching means for connecting said indicating means to said receiver, a magnetic relay for actuating nsaid' last named switching means to reverse saidrconn'ections, a source of alternating current, a circuit connecting said source to each of said magnetic relays, and a potentiometer and a, source of directeurrentA potential inparallel in the circuitVbetv/een said source and said rst named magnetic relay, said` potentiometer being calibrated to read in terms of bearing angles.

' AUGUST LETB. 

